The manufacturer may find it desirable to add any number of detersive and aesthetic ingredients to modern laundry detergent compositions using various handling techniques. For example, some sensitive ingredients such as enzymes and perfumes may be added by dry-mixing or by spraying onto a final granular product. The formulation of liquid detergents can involve various batch or continuous processes which may include various solubilizing, mixing, pH-adjusting, etc., steps. Such procedures have become well-known and commonplace in the detergent industry, and various batch, continuous and mixed continuous/batch processes for the manufacture of detergent compositions are currently in use.
Depending on the method of manufacture, the type of detergent composition being manufactured and the available equipment, it may be desirable for the manufacturer to employ various ingredients as stock solutions which are in fluid form. This is especially true when formulating liquid detergents. Typically, fluid forms of detersive ingredients comprise water or water-alcohol as the fluidizing medium in which the desired ingredients can be dissolved or slurried.
While detersive surfactants are mainly water-soluble, it is well-known to those skilled in the detergency arts that various surfactants often form quite viscous fluids, or even high viscosity pasty masses or gels, when added to water at high concentrations. Such high viscosity materials can be difficult to work with in a manufacturing plant. Of course, one simple method to avoid handling problems is either to work with such surfactants in their substantially dry, solid state, to use them in a more dilute, more easily handleable, fluid form, or to heat them to provide fluidity.
However, in the event the manufacturer wishes to employ surfactants in the form of fluids which are stable and relatively highly concentrated, it is generally advantageous to adjust such fluids so that they are easier to handle, especially with regard to their ability to be pumped using conventional pumping equipment. On the other hand, it would be undesirable to add any ingredients to such surfactant-containing fluids which could not be tolerated in the finished detergent compositions, since to do so would require additional steps in the overall manufacturing process to remove such unwanted ingredients.
The polyhydroxy fatty acid amides comprise one class of surfactants which are currently being investigated for use in detergent compositions. One problem with this class of surfactants is that concentrated aqueous solutions containing them tend to precipitate and/or gel on storage, even at elevated temperatures (35.degree.-60.degree. C.). Moreover, low temperature storage of this family of amide surfactants is of great importance, since at elevated temperatures they are susceptible to degradation via hydrolysis of the amide bond to give the amine and the fatty acid. For polyhydroxy fatty acid amides stored below 35.degree. C. this degradation is negligible, i.e., less than 5-10% per year, but at elevated temperatures it becomes highly significant, rising to about 10% per month at 50.degree. C. and about 20-25% per month at 60.degree. C.
Of course, it may be possible to employ various organic solvents to reduce the viscosity of concentrated solutions of polyhydroxy fatty acid amide surfactants. However, use of solvents such as ethanol, or even high concentration ethanol/water mixtures, can be problematic on a commercial scale due to issues involving government regulations, potential flammability and handling problems, and the like. Moreover, excessive amounts of even nonflammable solvents can be problematic since, if carried over into finished liquid detergent compositions, they can lower the viscosity of such end-product compositions to an undesirable extent. Accordingly, the use of high concentrations of organic solvents remains but a theoretical possibility to the commercial-scale detergent manufacturer.
Having due regard for the foregoing considerations, the present invention provides a method for preparing storage-stable, pumpable fluid compositions which contain relatively high concentrations of polyhydroxy fatty acid amide surfactants. Moreover, the invention provides such fluid compositions using ingredients which are either innocuous in the finished detergent composition, or which can provide desirable benefits to said finished compositions. Accordingly, removal of such ingredients is not required.